In such devices it may be appropriate to collect different variables such as, for example, the speed and the distance travelled in bicycles. For example, the current speed can give the rider an indication as to whether it is appropriate to select a specific speed-transforming gear speed or not.
However, for such a decision, it is appropriate to determine not only the speed, but also the currently applied torque in order to determine the force loading on the parts of the bicycle and the force which is applied by the rider and which is equivalent to the loading on his skeleton, musculature and joints. These variables can also be decisive for the selection of a transmission ratio or else for the decision to activate an auxiliary drive.
In addition, the power which is input into the drive shaft can be determined directly from the rotational speed of the drive shaft in conjunction with a measured torque.
Various possibilities for detecting the torque or torsion are known from the prior art, and a number thereof are also specialized particularly for application with driving cranks, in particular foot pedals in bicycles.
DE 102005018286 A1 discloses a device for determining a torque which is applied to a shaft, wherein a multi-pole magnetic ring is provided in a first shaft section of the shaft, and a stator mount with stator elements and fingers protruding in the axial direction is provided in a second shaft section. By means of a magnetic flux ring, magnetic fluxes are closed to a greater or lesser degree depending on the relative rotation of the shaft parts, with the result that the rotational angle, which is a measure of the torsional forces, is measured.
DE 10225018293 A1 discloses a torque sensor in which a magnet and a sensor unit are each independently attached to two sections of the shaft, wherein the sensor unit acts as proximity switch and indicates a rotation of the shaft as a change in position of the magnet.
DE 102005023182 A1 presents a torque-detection device having a torque-transmission plate for transmitting a torque between an engine output element and a torque converter drive element, wherein the transmission plate can easily be deformed elastically as a result of a torque by means of targeted weakened portions, and wherein strain gages for confirming the elastic deformation are provided on deformable webs of the transmission plate. Said document does not contain anything else about the functioning of the strain gages.
DE 102005041287 A1 presents a torque sensor comprising two component shafts, with each of the component shafts being connected to what is referred to as a recording tube and the recording tubes being coaxial to one another. They are permanently connected to the component shafts at points which are spaced apart from one another, and they have circumferential teeth on the end side so that given a greater or lesser degree of rotation of the shaft components the magnetic resistance between the recording tubes is periodically changed depending on the correspondence of the teeth. As a result, rotation of the component shafts with respect to one another can be detected. This is a measure of the acting torsional forces.
DE 10044701 C1 discloses a transmission device on the pedals of a bicycle, by means of which the pedal force is transmitted to the foot pedal. An elastic element in the form of a spring is compressed by the transmission of force, and this force effect is measured in order to determine the transmitted torque therefrom.
DE 69900898 T2 discloses, on the one hand, the connection of magnetostrictive elements for measuring torsion, wherein a magnetic material is intended to convert the torsion into an electrical voltage.
The main subject matter of the document is, on the other hand, the measurement of a torque by means of two commonly mounted disks which are coupled by means of spring elements acting in the rotational direction. The transmitted torque between the two disks can be determined by means of the angular offset which is achieved.
EP 1046893 B1 discloses basically the use of the magnetostrictive effect for the measurement of torque and the attachment of a magnetostrictive annular element to a shaft in order to transmit the torque and to utilize the effect. However, said document does not describe any structure which is directly related to the design of a roller bearing into which a torque sensor is integrated. For the measurement of the magnetic field, a specific sensor is described by means of which the current is measured at high frequency in the case of saturation magnetization of a probe in various magnetization directions, as a result of which the magnetic field of the magnetostrictive element can be measured precisely.